Definition - What does Additive Effects mean?
Additive effects are the resulting effect of two or more agents acting together. It is the sum of the effects of the individual agents. In relation to chemicals, additive effects are the sum of the effects of two chemicals when mixed together. Chemicals with similar chemical structures are usually combined, with no adverse effects resulting.
The sum of the additive effects are what you would be expect if you were exposed to each of the chemicals individually. Often, however there are synergistic effects, in which case, the combined effects are greater than each chemical by themselves.
Safeopedia explains Additive Effects
Additive effects are just one of three types of effects when chemicals are combined. Synergistic effects are when the combined effects are greater than those of each individual chemical. This can be dangerous, as each of the chemicals is able to work effectively on its own. An example of this would be combining alcohol with acetaminophen in your body. The combined effect could overwhelm the liver.
An antagonistic effect is when the combined effect of the two chemical is zero. In this case, the two chemicals cancel the negative effect of the other.